Presentation Date:
Tuesday, January 27, 2009
Location:
Photonics West 2009 (San Jose, CA)
Nano-scale periodic structures produce a greatly enhanced near-field at the surface and therefore they are very promising for applications involving Surface Enhanced Raman Scattering (SERS). The ideal shape of the structure is a sphere, a rod, a needle or a hemi-shell. Nano hemi-shell structures obtained by evaporating a thin metal film on small dielectric particles, in particular, have attracted much attention, because their resonant wavelength can be easily tuned by controlling the thickness of the metal film, shells diameter, or the distance between particles. Furthermore, the dielectric particles can be arranged on various kinds of substrates. We perform Raman spectroscopy to investigate the optical properties of 2D nano-hemi shell arrays composed of small polystyrene particles coated with gold. We measure the electric field distribution around the structure using femtosecond laser pulses, because their low energy minimizes thermal effects. We fabricate isolated clusters of two or three particles and hexagonally-arranged nano-hemi shells on a glass substrate. After fs laser pulse irradiation of the structures, only the regions of electric field enhancement near the hemi-shell structures are ablated. Our results agree with finite-difference time-domain simulation results, which allow us to visualize the electric field distribution around the hemi-shell structures.